<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      const user = {
        name: 'jack',
        age: 20,
      };
      console.log(user);
      Object.preventExtensions(user);
      // Object.seal(user);
      user.gender = 'boy';
      delete user.name;
      console.log(user);

      console.log(Object.isExtensible()); //false
    </script>
  </body>
</html>
